When electronic parts are mounted on a wiring circuit board on which a wiring circuit pattern is formed, generally an electronic part mounting land provided as part of the wiring circuit pattern is electrically connected to terminal electrodes of the electronic parts via a solder material.
For the purpose of preventing a phenomenon called “solder leaching”, a conductive intermediate layer is formed on a surface of the electronic part mounting land of the wiring circuit board by an electrolytic plating method or electroless plating method. The “solder leaching” is a phenomenon that a wiring circuit pattern formed on a wiring circuit board leaches into a solder material. In order to prevent the “solder leaching”, a method for forming a conductive intermediate layer as a barrier layer is often employed for solder-bonding electronic parts.
The conductive intermediate layer may be formed in consideration of its function of enhancing “solder wettability” between the solder material and the conductive intermediate layer in addition to the function of restricting the “solder leaching” phenomenon.
Conventionally, for the conductive intermediate layer, a bulk metal layer 3 formed on a conductive circuit layer 2 by a plating method is disclosed in Patent Document 1, for example.
Patent Document 2 discloses therein a technique for vacuum-depositing a metal such as copper on a circuit conductor layer 4 thereby to form a conductive metal layer 6 corresponding to the conductive intermediate layer.